1. Field of the Invention
The present invention relates to an ink-jet recording apparatus. In particular, the present invention relates to an ink-jet recording apparatus in which an ink introduced from an ink container is stored in a buffer tank, and the ink is supplied from the buffer tank to a printing head.
2. Description of the Related Art
An ink-jet recording apparatus has been hitherto known, in which a buffer tank is provided under an ink cartridge, and the ink cartridge and the buffer tank are communicated with each other via an ink supply passage and an air-introducing passage. Accordingly, the back pressure, which acts on the printing head, is maintained to be constant irrelevant to the remaining amount of the ink in the ink cartridge, and the remaining amount of the ink is detected in the buffer tank.
For example, Japanese Patent Application Laid-open No. 2002-307711 (for example, paragraphs 0055 and 0056, FIG. 3) describes an ink-jet recording apparatus including an air-introducing needle and a hollow ink supply needle composed of a conductive material for making communication between an ink tank (ink cartridge) and a buffer chamber (buffer tank), and a buffer chamber air-communicating section for making communication between the buffer chamber and the outside.
In the case of the ink-jet recording apparatus as described above, a difference is provided between the lower end levels or heights of the ink supply needle and the air-introducing needle. When the ink liquid surface in the buffer chamber is lowered as the ink is consumed by the printing head, then the air is introduced into the ink tank through the air-introducing needle, and the buffer chamber is replenished with the ink contained in the ink tank through the ink supply needle. Accordingly, the height of the ink liquid surface in the buffer chamber is made to be constant, and the back pressure, which acts on the printing head, is maintained to be constant irrelevant to the remaining amount of the ink in the ink tank. Further, the remaining amount of the ink in the buffer chamber can be detected by measuring the change of the electric resistance between the ink supply needle and the air-introducing needle.
In the case of the ink-jet recording apparatus as described above, the buffer chamber is constructed to have a sufficient volume on the assumption that the air in the ink tank may be expanded, for example, by any sudden temperature change, and the ink may be extruded from the ink tank to the buffer chamber. That is, the space having a sufficient volume is formed over the ink liquid surface in the buffer chamber. The ink, which is extruded from the ink tank, is accommodated in the space as described above so that the ink is prevented from any leakage to the outside.
However, in the case of the ink-jet recording apparatus as described above, the space having the large volume is formed over the ink liquid surface in the buffer chamber. Therefore, the following problem has arisen. That is, the area of the ink liquid surface is increased corresponding thereto, and the amount of water evaporation from the ink liquid surface is increased. As a result, the following problem has arisen. That is, for example, when the ink-jet recording apparatus is left to stand for a long term, then the viscosity of the ink is increased, and it is impossible to smoothly perform the operation for supplying the ink to the printing head and the operation for discharging the ink from the nozzles.
When the area of the ink liquid surface is large, the lowering amount of the height of the ink liquid surface is decreased with respect to the consumption of a certain or constant amount of the ink. Therefore, a long period is required for the ink liquid surface to make sufficient separation from the electrode (air-introducing needle). Therefore, the following problem has arisen. That is, any erroneous judgment which shows the presence of the ink is made when the breakage of the electric conduction between the ink supply needle and the air-introducing needle is once detected, and then the electric conduction is made again due to any fluctuation of the ink liquid surface.